1. Field of the Invention
The present invention relates to an optical recording medium and an optical recording method using said medium. More particularly, the present invention relates to an optical recording medium for use as a portable information recording media which allows optical recording and reading of information, such as optical disk, cash card, credit card and ID card, as well as to an optical recording method using said medium.
2. Related Background Art
The conventionally known methods for recording information on an optical recording medium is by applying laser beams thereto to alter its condition are largely divided into the following two methods.
The first method is one utilizing a phenomenon that an optical recording medium, when irradiated with laser beams of TiO.sub.2, chalcogenide glass or the like, generates heat and thereby causes a phase change between an amorphous state and a crystalline state.
However, this method is defective in that the amorphous nature of the optical recording medium used is gradually lost due to its spontaneous crystallization, tending to regenerate wrong information.
The second method is one disclosed in, for example, Japanese Patent Application laid-Open No. 17139/1982, which comprises applying laser beams to a recording layer consisting of an absorptive layer composed of an organic dye (e.g. squalene, naphthoquinone) and a reflective layer placed thereon and composed of a low-melting metal (e.g. Bi, Te), to cause the deformation of the recording layer, removing the deformed portions to form pits, and recording information in these pits.
In this method, reading of recorded information is conducted by detecting the change of reflectivity or transmittance. However, the method is defective in that excessive or insufficient deformation takes place in formation of pits making their shape unstable. Further the types of raw materials usable for the recording layer are restricted.
Optical recording methods wherein no pit is formed have been proposed recently.
For example, Japanese Patent Application Laid-Open No. 127937/1981 discloses a method which comprises applying laser beams to an optical recording medium consisting of a substrate, an intermediate layer placed thereon and composed of an organic material and a metal layer placed on the intermediate layer to heat the intermediate layer, allowing the intermediate layer to absorb the heat and thereby to cause swelling and to form protuberances, and recording information in these protuberances.
However, this method is defective in various respects. That is, the optical recording media has poor durability because the protuberances which are formed on the substrate and wherein information is recorded tend to deform due to external pressures; the metal layer must be thick in order to prevent the leakage of the gas generated by foaming to form protuberances and accordingly a large energy is required to enable recording of information; moreover, the protuberances wherein recording is made tend to have an unstable shape.